1. Field of the Invention
The present invention relates to apparatus for dispensing particulate solids which agglomerate together to prevent free flow in precisely metered quantities.
2. Description of the Prior Art
It has been known that particulate solids may be emptied from a container by inclining the container to a vertical orientation at which the particles break loose and flow under the influence of gravity. Flowing of the solid continues until the vertical angle of inclination is reduced to a point at which frictional forces between the individual particles within the solid cause the particles to bridge together. The problem with dispensing free flowing solids with the aforementioned method is that it is impossible to precisely meter the flow rate once the individual particles have started to flow. Moreover, it is difficult to stop the flow of solids precisely after a predetermined or desired weight of solid has been dispensed from the container.
The foregoing method is even more difficult to use with dispensing solids in which the individual particles readily agglomerate together to form bridges which prevent flow. The agglomerating property makes it much more difficult to initially break apart the bridging of the individual particles. Moreover, once free flow has started, the property which causes agglomeration makes it difficult or impossible to maintain a uniform flow rate and to stop the flow of solids at a precise point.
Systems are also known for dispensing particulate solids from conical-shaped hoppers by the application of an agitating force with sufficient energy to cause the free flow of the solid out of the bottom of a conical hopper. Systems of this type are disclosed in U.S. Pat. Nos. 3,178,068, 3,323,492, 3,270,463, 3,278,081, 3,785,529 and 3,791,558. None of the systems disclosed in the aforementioned patents provides a mechanically simple system for precisely metering the flow rate of particulate solids.
U.S. Pat. No. 3,865,278 discloses a laboratory feeding device for particulate material. A vertically disposed tube is connected to a container of a particulate material by means of a coupling at which a screen is located through which the particulate material falls into a feeding trough which moves the material to a discharge end thereof under the influence of applied vibrations. This system is not satisfactory for dispensing solids which tend to agglomerate for the reason that the transporting mechanism has a V-shaped cross section which concentrates the particulate solids into a confined area which promotes agglomeration of particulate substances which tend to agglomerate and prevents the dispensing of a precise weighed amount. Moreover, the disclosed system does not have any mechanism for reducing the rate of flow for precisely metering of the weight being dispensed at the end of a dispensing cycle.
Solution preparing devices are disclosed in U.S. Pat. Nos. 4,345,628, 4,350,186, and 4,469,146 which meter the weight of a dispensed liquid to be used in preparing a desired type of solution. A total weight of the desired solution including the liquid to be dispensed is calculated. The dispensing of the liquid is stopped when the actual weight of the solution equals the calculated weight. The rate of dispensing of the liquid is reduced when the actual weight approaches the desired weight to facilitate the stopping of dispensing at precisely the calculated weight.